Thread: understanding fertilizer a little better

I've got a question, when they say you want 1lb of N per 1,000 sq ft, you take 100/(first number on bag of fert.) and you get how many pounds of product you want for each 1,000 sq. ft. So why does it matter if the N number is 18 or 30. You will need less product if you use a 30 nitrogen bag.

18N you need 5.55 lbs of fert per 1,000

30N you need 3.33 lbs of fert per 1,000.

Same goes with P. So I guess my question is, is there a difference if you use a 18-24-6 vs a 30-24-4 and use the calculations?

Riggle's right that there's no difference in the products (judging by just the analysis) -- all you have to do is adjust your spread rate. So, you will need more of the 18%N product to deliver as much N as the 30%N product.

But, not all is equal for the rest of the analysis. Applying 18-24-6 at 1#N/M gives you 1.33# P2O5/M and 0.33 #K2O/M, while the 1#N/M of 30-24-4 gives you 0.8# P2O5/M and 0.13# K2O/M.

So, the 18%N product might fit better for you if you need more P and K, while the 30%N product might work better if you need a little less P and K.

Look at your minor package % also. Those are very important. Type of minors
like oxides, sulfates, sucrates. The carrier for the nutrient can matter based on soil type.

Also watch your cost per 1000 sq. Not cost per bag.
If the two blends you mentioned were $12 for the 18-24-6 and $20 for the 30-24-4. Based on 1# of N per 1000sq ft. They would both cost $1.33 per thousand sq ft.Posted via Mobile Device

By law the slow-release percentage must be listed and usually the source of the slow release properties. But the label may exaggerate or might try to fool you by saying, "contains 15 percent slow-release nitrogen". Or it may say, "Contains 50 percent sulfur-coated urea".
15 percent slow-release does not mean on top of the 30 percent already specified--rather you have 15 percent slow release and 15 percent fast release; total 30.

Some professionals want a low percentage of chloride, (want no muriate of potash).

And 50 percent sulfur-coated urea is not exactly 50 percent slow release--some of the "coated " fert is not slow release due to normally a percentage of the granules are cracked open. Read the label carefully and be a bit skeptical. I don't know if there is such a thing as slow release phosphate. Slow release potash is rare.